Treatments for nausea and vomiting can include some oral medications, rectal suppositories, and IV combinations. Through compounding new routes of administration or combinations can be made, including transdermal and intranasal routes.
https://www.ncbi.nlm.nih.gov/pubmed?term=8625179 

Intranasal metoclopramide.
https://www.ncbi.nlm.nih.gov/pubmed?term=10473023 

Nasal absorption of ondansetron in rats: an alternative route of drug delivery.
https://www.ncbi.nlm.nih.gov/pubmed?term=10803929

Bioavailability of Promethazine in a Topical Pluronic Lecithin Organogel: A Pilot Study
https://www.ijpc.com/abstracts/abstract.cfm?ABS=2203

Problems like dry mouth, stomatitis, and mucositis are common in cancer patients and other populations. By treating these ailments at the site of the problem with compounded mouthwashes, solutions, lozenges, and topical products the patient is able to receive relief without as many side effects of other therapies. Use of orally administered anhydrous crystalline maltose for relief of dry mouth.
https://www.ncbi.nlm.nih.gov/pubmed?term=11246934 

Oral glutamine reduces the duration and severity of stomatitis after cytotoxic cancer chemotherapy.
https://www.ncbi.nlm.nih.gov/pubmed?term=9762946

Allopurinol mouthwashes in the treatment of 5-fluorouracil-induced stomatitis.
https://www.ncbi.nlm.nih.gov/pubmed?term=8192112

Topical Morphine for Oral Mucositis in Children: Dose Finding and Absorption.
https://www.ncbi.nlm.nih.gov/pubmed?term=22658469 

For patients with migraines finding a successful treatment without side effects can be difficult.  Combination drugs may be helpful, but a commonly used one, Midrin, is not currently available. Another common treatment includes triptans, like sumatriptan, which may cause serious cardiovascular side effects.  Compounding can offer other treatment options or replace ones not on the current market. Efficacy of a fixed combination of indomethacin, prochlorperazine, and caffeine versus sumatriptan in acute treatment of multiple migraine attacks: a multicenter, randomized, crossover trial.
https://www.ncbi.nlm.nih.gov/pubmed?term=12940804

Neuropathic pain, often caused from another condition like diabetes or shingles, can be incredibly painful and often debilitating. Often this pain does not respond to traditional painkillers and requires some other form of therapy.  Compounding can expand options for treatment to help the patient find a treatment that works for them.

Successful treatment of postherpetic neuralgia with oral ketamine.
https://www.ncbi.nlm.nih.gov/pubmed?term=7833583 

Combination of alpha lipoic acid and superoxide dismutase leads to physiological and symptomatic improvements in diabetic neuropathy.
https://www.ncbi.nlm.nih.gov/pubmed?term=22329607